You may as well ask why you should look anywhere but at your own feet while walking around your city.
You have been told that every new OS update brings new features and abilities, and Apple publishes an iPhone User Guide for learning about iOS features like how to change the default mail app (https://support.apple.com/guide/iphone/change-the-default-ap...). It's on you to look.
It's about 5 years old by now. Not having looked for something in a couple of years and being bummed out by that doesn't make Apple the bad guy.